I recently assembled my new bottom end, and Ive noticed something weird...

First off, setup consists of b18a bottom end, NuFormz block guard, balanced B18B crank, Eagle big bolt rods, and CP 81.5mm pistons, assembled with Clevite 77 bearings......

My question... When I start the car to get it warmed up, it makes a knocking sound, almost like a slight rod knock... But after driving for a bit to warm it up, and going in to boost a few times, it seems to go away... I am thinking its just piston slap due to the piston to wall clearance CP reccomends, and a couple other people have told me it appears to be just that...

My question is, has anyone else experienced this with the CP pistons???

All the machine work was done by a top notch machine shop, and was all done to CP's factory specs...

Im just trying to rule out rod knock, and so far this seems to be the most logical answer....

 

I have CP's and it doesnt do that on my car.

 

It still sounds like piston slap, if it did it all the time then I would start to worry.

 

forgrd pistons make a lot of noise when they are cold

 

My CP's make a little noise when cold as well. I should have measured the skirts and compared them to the bore size to make sure it was dead on, but I'll admit, I was lazy. Next build will be much more controlled.

 

shouldn't be making a knock noise .. i have gone through two sets of CP's 84mm and 84.5, maybe you have spun a rod bearing, are you using the right weight of oil? if it continues, maybe you should pull the head off, hopefully the shop bored the block to CP specs and ring gaps specs. Alot of times they will skip or neglect the ring gap specs. I know, I won't mention who, but i've seen a pretty well known tuner and builder in Socal do this.

 

I'd almost guarantee that you are being overly paranoid. All motors with forged pistons are noisy when they are cold compared to stock motors. Just be glad that you didn't use Arias pistons, those sound almost like a diesel. It really depends on how loud the noise is. Also, is the car doing anything else wierd?

 

the noise sounds like a really light knocking, or a valve tap, but its not real consistant like a rod bearing would be, and as i said, once the motor sees boost a couple times and gets warm, it usually goes away... With all of my experieces, a rod knock sound would be constant, get louder at higher rpms, and not go away once warmed up... PLUS, My oil pressure is perfect... With a spun bearing I would expect lower oil pressure.....

 

It really sounds more like piston slap than anything else. My CP's don't slap at all, but your tolerances might be a lil looser.

Usually valvetrain noise as well as a spun rod bearing would make a constant knocking sound. It's good to be a lil **** on a new build.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BodyKits NW &raquo;</TD></TR><TR><TD CLASS="quote">It really sounds more like piston slap than anything else. My CP's don't slap at all, but your tolerances might be a lil looser.

Usually valvetrain noise as well as a spun rod bearing would make a constant knocking sound. It's good to be a lil **** on a new build. </TD></TR></TABLE>

A little ****??? hahaha... I thouroughly investigate any noise, or any drop of fluid i find... This is the first bottom end I have built on my own, so Im just being a little cautious about everything until i know all is well, so I can trust my ability to do it properly... I did everything according to the helms manual, and everything was spec'd correctly, and all tolerances were good when i plastiguaged the bottom end, so I'm thinking its just piston slap... It would just be nice to get a definite answer for some reassurance for my peace of mind...

 

My old motor with SRP's slapped. But my new motor with Wiseco makes no noise. Ive heard other Wiseco motors and they are all pretty quiet. My friends 4g63 with CP's was pretty quiet too. Maybe you made the piston to cyl wall a little too big?

liam

 

The machine shop had the spec sheet from CP, and I told them to do everything to those specs, so unless they fucked up it should be perfect... The spec sheet from CP reccomends 0.0035 piston to wall clearance...

 

It does sound like piston slap. You need to know specifically what the bore is to determine if that is the problem.

 

It has to just be slap because CP's are very quiet from what ive seen.

 

aren't the clearances already factored into cp pistons...making them a zero clearance piston? i mean like if they are 81.5mm, the bore should be EXACTLY 81.5mm???

 

The spec sheet from CP says "bore diameter : 3.209, clearance : 0.0035"

Im holding the sheet in my hand right now... I guess I will have to call the machine shop tomorrow to be sure they did exactly that... If I dont have this figured out soon, its going to the shop Monday or Tuesday to be thoroughly inspected by my mechanic....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by m R g S r &raquo;</TD></TR><TR><TD CLASS="quote">aren't the clearances already factored into cp pistons...making them a zero clearance piston? i mean like if they are 81.5mm, the bore should be EXACTLY 81.5mm???</TD></TR></TABLE>

I dont believe there can be such a thing as a zero clearance piston... Think about it, pistons are made of metal, motors make heat, heat expands metal... Granted, some pistons expand differently due to different levels of silicone, but all expand as far as i know....

 

Your bore should be EXACTLY 3.209" (81.5mm)
Any more and you could be subject to slap
Piston would measure 3.2055
Therefore .0035" clearance

 

So if what I am experiencing is indeed piston slap, will this damage my motor??? Ive seen many cars that have really loud piston slap, mainly JEs, but they run fine... They just sound like diesel trucks at idle...

 

Noise does not sound like a good thing to me. Not sure how much it will effect piston life.

 

Well, looks like Im just gonna take it to the shop Saturday mornin and put it up on the lift... I'll just drop the pan, etc., and inspect everything from under the car, to at least rule out a bearing issue...

 

I came over today to help with the final tune. It sounds like piston slap to me but it's excessive at points and varies given the conditions. I guess the only thing he can do is drop the pan AND call the machine shop Monday. I'm going to start building a motor for someone next week and will be using the same machine shop. I will check over the bore when I get the block back from the machine shop. Until Monday ... ... ...

-- 0x64 / John

 

The car feels good. I got partial throttle 90% tuned and the boost portions of his maps up to 12lbs tuned for the most part. The car feels good but he needs to figure out the spiking issue this week before we go any further. If not we will figure it out next weekend. My only idea right now is the boost controller.

Cant wait to hear from the machine shop tomorrow. Don't forget to call them

 

Im going to contact TurboSmart, and see if there are any other known problems with people using this boost controller, and maybe try it on someone elses car...

And I will be calling the machine shop tomorrow, as well as taking it to Collin to see what he thinks about it....

 

What machine shop did you use ?

Collin isnt going to be able to tell you **** besides, it sounds like piston slap